Review Questions:

2)	physics is a branch of science that studies the most general principles 
	underlying the natural world.

6)  	According to the earlist greek theory, planets move at a uniform rate around Earth.
	However,a careful observer can realize that planets are  moving nonuniformly 
	relative to the background stars. 

17)     Tycho Brahe worked with accurate devices to take data on the motion of 
	the planets. Brahe's accurate measurments (used by Keplar) showed that 
        theories of Copernicus and Ptolemy were flawed. 

20)	In science, we learn from experience, as in life. Science is objective,
        hypothesis proved by performing experiments and making measurements. 
        Here it differs from art which is largely subjective.

Conceptual Exercises:

2)	diagram:

14)	Each theory uses the concept of eccentricity. 

20)	Both Ptolemy's Earth-centered theory and Copernicus's sun-centered theory correctly
	predicted the (then) known data. 

21)	Theories must always agree with the data. An aesthetic argument like this doesn`t have any
	place in science. 


30)     1million / 100 billion = 0.00001

32)	4LY/ 8min = 4*365*24*60 / 8 = 262800 AU